FLOURITE

Also known as flourospar, it is a member of the halide group which is very variable in colour. It may be blue, green, purple or yellow and may contain banding. It is fairly soft (4 on mohs scale) and twinning may be evident. It is also very sensitive to heat. It's name is derived from the Latin word fluere which means to flow and refers to it's low melting point.

Flourite is primarily used in indusry particularly in iron smelting and ceramics. Some pieces are used in jewellery but due to it's softness may be capped with a protective layer of rock crystal. It is also a major source of flourine gas and hydrofluoric acid.

Although it is usually pure sometimes some calcium may be replaced by yttrium. This is known as yttrium flourite and is usually violet. Blue flourite found at a particular location in Derbyshire, England is known as Blue John.

It may be found in hydrothermals and around hot springs possibly in association with lead and silver. It may also be associated with calcite, barite, celestine or dolomite.

Main locations include Germany, Tuscany (Italy), Switzerland and Colorado (US). In the UK it may be found in Cumbria, Durham or Derbyshire (Blue John).

FUCHSITE

A silicate which is green due to the presence of chromium oxide impurities. It is a variety of muscovite and is a member of the mica group. It is named after Johann Nepomuk Fuchs, a German Geologist who studied mica minerals. It is very soft (2 on the mohs scale).

Mariposite is a mica mineral named after Mariposa California which has exactly the same formula but never contains more than 1 per cent chromium oxide. It is very similar to fuchsite.

Fuchsite is found in metamorphic rocks (particularly dolomites) and mica schists where it may be associated with biotite.

It may be found in Austria, Italy and the Ural mountains (Russia). It's purity is determined by comparison with specimens from Schwarzenstein in Austria which is the original source of fuchsite.